1. Technical Field
This invention relates generally to pumps, and more particularly to a pumping system designed to better accommodate varying loads.
2. Background Information
One problem encountered with some pumping systems, such as a conventional gear pump driven by a constant speed electric motor, occurs when pumping liquids having different or varying viscosities, such as epoxy, lacquer, paint thinner, syrup, and the like. Not only do the viscosities of such liquids differ from each other, but the viscosity of any one may vary significantly with various changing conditions such as temperature. In addition, it may be desirable to pump the liquid through differently sized lines and this causes load variations as well. As a consequence, the pumping system must be designed to accommodate the varying load that can result because a system failure may have catastrophic consequences if it occurs when pumping a liquid such as epoxy that can quickly solidify in the pump and conduits.
To guard against that happening, some existing systems utilize a motor of sufficient size to handle the greatest load anticipated (i.e., that accompanying the greatest viscosity and smallest conduit or line expected). However, processing speed is then restricted to that which is safe under such worst case conditions so that in addition to such a technique being costly in terms of hardware, it is inefficient in terms of processing speed. Consequently, it is desirable to have a pumping system that alleviates these concerns.
A related problem occurs when the flow of liquid out of the pumping system is turned on and off, such as may occur in the normal course of such activates as packaging. Turning the flow of liquid off, for example, can cause an abrupt increase in the load and pressure. This only compounds the varying-load problem caused by different and varying viscosities.
Some existing systems avoid this problem by either simultaneously turning the motor on and off or by switching in a bypass arrangement that provides a path from the pumping system outlet back to the inlet. However, turning the motor on and off can be inconvenient and decrease processing speed, Furthermore, it can involve high starting currents each time the electric motor is turned back on. The use of a bypass arrangement also results in significant current fluctuations, a high pressure head tending to build up during bypass and a fluid surge occurring when the system outlet is opened again. Thus, it is desirable to have a system that alleviates these concerns also.